This invention relates to an image pickup device used for a movie camera, a still camera (shutter camera) and the like, and more particularly to an image pickup device having a high resolution.
A video signal which is obtained by picking up an optical image of an object on an image pickup device can be easily subjected to editing, trimming and any other video signal processing. In addition, such a video signal can be easily recorded and reproduced using a reversible recording medium capable of erasing a recorded signal. On the other hand, image pickup devices conventionally used for generation of the video signal have such an arrangement to convert an optical image of an object formed on a photoelectric conversion area of an imaging element by use of an imaging lens to electrical image information corresponding to the optical image of the object at the photoelectric conversion area of the imaging element to sequentially output such an electrical pictorial image information on a time base as the video signal. As is well known, various kinds of pickup tubes and various kinds of solid state image sensors are used as the imaging element of the image pickup device.
Recently, there is much demand to reproduce a picture with both picture quality and resolution considerably higher than those of the currently utilized television systems. In accordance with such a demand, novel systems, e.g., the so-called Extended Definition Television (EDTV) and High Definition Television (HDTV) systems, etc. have been proposed for this purpose.
In order to obtain a picture of high picture quality and high resolution, an image pickup device capable of generating such a video signal to permit a reproduction of the picture with high picture quality and high resolution is required. In the case of the image pickup device which uses a pickup tube as the imaging element, however, the realization of the high resolution by reducing the electron beam diameter cannot be expected because there is a limitation for reducing a diameter of an electron beam in the image pickup tube. Further, since a target capacity of the pickup tube increases with the target area, the realization of high resolution due to an increase in the target area is impossible. Furthermore, in the case of the image pickup device for use in taking moving pictures, a frequency range of the video signal becomes several tens of MHz to several hundreds of MHz and this causes problems in view of the S/N ratio. For these reasons, it is difficult to generate a video signal which enables the reproduction of pictures with high picture quality and high resolution by using the above-mentioned image pickup device.
The above-described problems will be described in an actual sense. Namely, in order to generate such a video signal capable of reproducing a picture with the high picture quality and high resolution by means of an image pickup device using an image pickup tube as the imaging element, it is conceivable to reduce the diameter of the electron beam of the image pickup tube, or to use a target having a large area. However, since there is a limitation in reduction of the diameter of the electron beam of the image pickup tube due to the performance of an electron gun of the image pickup tube and the structure of the convergence system, there is a limitation in the realization of the high resolution due to reduction of the diameter of the electron beam. Moreover, when an attempt is made to use an imaging lens having a large pickup image size to provide a high resolution by increasing the area of the target, the high frequency signal component of an output signal from the image pickup tube is lowered due to an increase in the target capacity of the image pickup tube caused by increasing the target area, resulting in a considerably lowered S/N ratio for the image pickup tube. Thus, some image pickup devices using image pickup tubes are unable to satisfactorily generate video signals that can reproduce pictures with the high picture quality and high resolution.
On the other hand, for reproducing a picture of high picture quality and high resolution by means of an image pickup device using a solid state image sensor as the imaging element, it is required to use a solid state sensor having a large number of pixels. However, a clock signal which drives the solid state image sensor having the large number of picture elements naturally requires a high frequency. For example, in the case of image pickup devices for use in taking moving pictures, the clock signal for driving the solid state image sensor has a high frequency in the order of several hundreds of MHz. In addition, an electrostatic capacitance of the associated circuit which is driven increases as the number of picture elements increases. Since an upper limit of the frequency of the clock signal for driving the solid state image sensor is presently believed to be approximately 20 MHz, it is virtually impossible from a practical point of view to use such a solid state image sensor as the imaging element.
As has been described above, in the conventional image pickup device, it is impossible to satisfactorily generate a video signal which gives a reproduced picture with high picture quality and high resolution, due to the limitations of the imaging element indispensable for constituting that image pickup device.
In view of this, the assignee has already proposed, as an image pickup device capable of solving the above-described problems, an image pickup device including a photo-to-photo conversion element comprising at least a photoconductive layer member, a dielectric mirror and an optical modulation layer member which are disposed between two transparent electrodes, to therefore form an optical image of an object on the photo-to-photo conversion element by an imaging lens to read out, by using light, from the photo-to-photo conversion element, optical image information corresponding to an optical image of the object to record it on a storage member.
However, in the case of memorizing, on the storage member as a two-dimensional configuration, optical information corresponding to the optical image of the object which has been read out using light from the photo-to-photo conversion element, the storage member must be transported by an intermittent drive like a transportation or carrier mechanism for an ordinary movie film. Thus, the carrier mechanism for storage member becomes complicated, resulting in the requirement to take countermeasures therefor.